The present invention relates to a braking device, of the type used to provide the driver of a vehicle with assisted braking.
Such braking devices are generally composed of a master cylinder and of a pneumatic booster, the booster comprising, in particular, a rigid casing, a mobile partition delimiting at least a front chamber and a rear chamber, in sealed fashion, inside the casing, a three-way valve that can be actuated by a control rod in order, selectively, to let different pressures into the front chamber and the rear chamber and correspondingly subject the mobile partition to a boost force acting in the direction of the master cylinder, and a push rod connected to the mobile partition for operating the master cylinder, the casing comprising a front shell secured to the master cylinder and forming a wall for the front chamber, and a rear shell forming a wall for the rear chamber, the front shell and rear shell each comprising a radial shoulder, cohesion between the front shell and the rear shell being ensured by hooping interacting with the shoulders of the front shell and rear shell.
Devices of this type are well known in the prior art, as represented, for example, by patent document GB-A-2,136,520. They are usually placed in the front compartment of a motor vehicle, generally containing the vehicle engine, the booster being fixed by its rear wall to the bulkhead that separates this front compartment from the passenger compartment, and the master cylinder being fixed to the front wall of the booster. The booster control rod passes through an opening in the bulkhead and is operated by a brake pedal in the passenger compartment.
Over recent years, a tightening of safety standards has revealed the need for motor vehicle braking devices, and in particular boosters, to evolve in such a way that a frontal or oblique impact applied to the vehicle cannot readily be transmitted to the driver""s leg, even if the impact occurs while the driver is depressing the brake pedal as hard as he can.
What happens is that in the event of a frontal or oblique impact of the vehicle with another vehicle or with a stationary obstacle, the structure and bodywork of the vehicle are designed to deform progressively in order to absorb the greatest possible amount of the energy involved in this collision.
It is nonetheless often the case that the engine, or the load being transported in the front compartment of the vehicle, is pushed back under the effect of such a collision, and comes to interfere with the master cylinder. Such interference may result in the application to the master cylinder of a force directed along its axis, or of a force which makes a certain angle with its axis. In all instances, the result is, however, that the master cylinder, via its fixing flanges, urges the casing of the booster back towards the vehicle bulkhead.
It therefore follows that the consequences of a frontal or oblique impact are, on account of the layout of the boosted braking device in the front compartment of the vehicle, first of all that the bulkhead is made to move back under the action of the booster casing, whether or not the booster is equipped with tie bolts, and also that the brake pedal, is made to move back, possibly causing serious injury to the driver of the vehicle. The internal arrangement of this compartment, especially when it contains a vehicle engine, is always practically specific to this vehicle, which means that a solution that can be used successfully in a given vehicle for avoiding the brake pedal being made to move back may prove devoid of any positive effect in some other vehicle.
The invention falls within this context and its object is to propose a new solution, capable satisfactorily of limiting the transmission of a frontal or oblique impact in configurations where the known solutions do not prove sufficiently effective, by providing a boosted braking device such that interference from the engine or the load being transported in the front compartment of the vehicle with the master cylinder is not converted into the brake pedal being thrown back towards the driver of the vehicle, and which can be achieved without using additional components which would lengthen the axial length of the braking assembly forward of the bulkhead.
To this end, the device of the invention is essentially characterized in that the hooping comprises at least two part hoops, the part hoops being joined together by at least one locking element capable of being rendered non-functional when the master cylinder is subjected to substantial stress as a result of a frontal or oblique impact of the vehicle.
Thanks to this arrangement, the front and rear shells of the booster may, in the event of an impact, become detached from one another without transmitting substantial force towards the driver, the detaching of these two parts even fulfilling the function of absorbing some kinetic energy.
According to a possible embodiment of the invention, the part hoops each comprise, at least at one of their ends, a tab extending radially towards the outside of the booster, the adjacent tabs of two consecutive part hoops being held against one another by the locking device.
For example, the locking device comprises a fork formed at one end of a rigid bar, the other end of which is secured to the front shell of the booster.
In an advantageous arrangement, the end of the rigid bar is secured to a plate itself secured to the front shell of the booster.
In this case, the plate may be inserted between the front shell of the booster and a fixing flange of the master cylinder.
Provision may also be made for the end of at least one of the part hoops to be formed with a tab forming a hook intended to interact with a tab of the adjacent part hoop and extending radially towards the outside of the booster.
Other objects, features and advantages of the invention will emerge clearly from the description thereof given hereafter by way of non-limiting indication with reference to the appended drawings.